Process of bleaching raw heavy spar



Patented Apr.16 ,1929. 4

UNITED STATES PATENT OFFICE.

KARL EBEItS, F AHRENSBURG, HOLSTEIN, GERMANY.

PROCESS OF BLEACHING RAW HEAVY SEAR.

I No lirawing. Application filed July 18, 1925, Serial No. 43,409, and in Germany July 17, 1924.

My invention relates to improvements in the process of bleaching raw heavy spar, and more particularly in the process in which the heavy spar is bleached by means of suitable acids such as sulphuric acid. As is known to those skilled in the art the foreign matter contained in the heavy spar consists having a very pure white color after being ound is of high economical value, and it is important to bleach low grade heavy spar so as to produce a pigment of a pure white color.

I have discovered that when bleaching heavy spanby means'of sulphuric acid in the presence of a certain proportion of fluor spar, a material is produced which has a perfectl white color. Therefore my invention consists in breaking up or grinding heavy spar already containing a suitable'proportion of fluor spar or breaking up or grinding heavy spar containing fluor spar and adding thereto a certain amount of fluor spar, and heating the said heavy spar and fluor spar in sulphuric acid. In such cases in which the heavy spar is very impure I prefer .to roast the mixture of heavy spar and fluor spar at a temperature below sintering,

before treating the same by means of sulphuric acid. This renders certain of the impurities more readily removable by the subsequent treatment.

Example 1.-A raw heavy spar having a verydark color and containing about 6 per cent of fluor spar is disintegrated and brought into boiling sulphuric acid of 20 per cent strength, and boiled therein about half an hour. After boiling, the material is washed by means of water. The result is a perfectly white bleached spar.

Example Q..A very impure heavy spar is intimately mixed with 5 per cent of fluor sp ar, the mixture is heated to a temperature below sintering temperature, the roasted mixture.

is stirred in one fourth of-its weight of sulphuric acid of 20 per cent strength, and so much water is added that the mixture can be stirred. After boiling, the material is washed by means of water.

To test the effect of the fluor spar in the process, the heavy spar treated according to example 2 has (in another experiment) been subjected to the same process, (mixing in 20% H SO adding water and boiling, and Washing) but without adding fluor spar. I have found that even after one hour a satisfactory bleaching was not obtained.

a I presume that in the process hydrofluoric acid is set free, which acid has an important effect in breaking up or destroying and removing the foreign matter.

I have found that the effect can be further improved, and more particularly with reference to organic foreign matter, when adding slight amounts of niter to the mixture of heavy spar and fluor spar, the said niter being i .added either before roasting orafter roasting and before subjecting the mixture to the action of the sulphuric acid.

Preferably the hydrofluoric acid produced in the process is recovered b means of alkalies or heavy spar contaimng chalk. function of the niter introduced into the process is based on the formation of nitric acid by means of the sulphuric acid. Therefore the same result may be attained by using sulphuric acid containing a certain amount of nitric acid.

I claim:

1. The herein described process of producing white heavy spar from raw heavy spar,

The

which consists in treating the said heavy spar in the presence of fluor spar with sulphuric acid, and'washing by means of water.

2. The herein described process of producing white heavy spar from raw heavy spar, which consists in treating the said heavy spar in the presence of fluor spar with sulphuric acid of about 20% strength at elevated temperature, and washing by means of water.

3. The hereindescribed process of producing white heavy spar from raw heavy spar,

which consists in roasting heavy spar in the presence of fluor spar, treating the said mixture with sulphuric acid, and washing by means of Water. I

.4. The herein described process of producing white heavy spar from raw heavy spar, which consists in roasting heavy spar inthe presence of fluor spar, treating the roasted.

product at elevated temperature with sulphuric acid of about 20% strength, 'and Washing the same.

5. The herein described process of producing white heavy spar from raw heavy spar,

' which consistsin roasting heavy spar in the presence of fluor spar ata temperature below sintering tem erature, treating the said mixture with su phur'ic acid, and Washing by means of water. I

\ 6. The herein described process of producing white heavy spar from raw heavy spar, which consists in treating the saidheavy spar in the presence of fluor sparand niter with sulphuric acid and washing by means of water. 1 7. The herein described process of producing white heavy spar from raw heavy spar,

- which consists in roasting heavy spar in the presence of fluor spar and niter, treating the said mixture with sulphuric acid, and washing by means of water.

8. The herein described process of producing white heavy spar from raw heavy spar,

which consists in treating the said heavy spar in the presence of fluor spar with sulphuric acid in the presence of nitric acid, and thereafter washing by means of water.

9. The herein described process of producing white heavy spar from raw heavy spar, which consists in treating the said heavy spar in the presence of a fluoride with sulphuric acid, leading the gases given off in the reaction into contact with a'compound of an alkali-forming metal capable of absorbing hydrofluoric acid with the formation of a fluoride, and treating suchfluoride and a new lot of heavy s ar'with sulphuric acid, whereby the hydro uoric acid is regenerated. v p

In testimony whereof I hereunto aflix my signature.

KARL EBERS. 

